Container for liquefied gases at cryogenic temperatures

ABSTRACT

A device is provided for containing liquefied gases at cryogenic temperatures in a tanker vessel. The container device includes a primary tank for containing the liquefied gas and a drip pan formed as an integral part of and below the primary tank for collecting and retaining quantities of the liquefied gas that may leak through the primary tank and for providing support for the primary tank. A spray shield acting as a liquid tight barrier is spaced apart from and structurally supported by the primary tank. The drip pan includes a plurality of apertures in fluid communication with the space between the primary tank and the spray shield for enabling the passage of seepage from upper portions of the primary tank through the space and into the drip pan.

[ Oct. 23, 1973 Primary Examiner-Duane A. Reger Assistant Examiner-E. R. Kazenske Attorney-Manahan and Wohlers and F. Donald Paris 571 ABSTRACT A device is provided for containing liquefied gases at cryogenic temperatures in a tanker vessel. The container device includes a primary tank for containing the liquefied gas and a drip pan formed as an integral partof and below the primary tank for collecting and retaining quantities of the liquefied gas that may leak through the primary tank and for providing support for the primary tank. A spray shield acting as a liquid tight barrier is spaced apart from and structurally supported by'the primary tank. The drip pan includes a plurality of apertures in fluid communication with the 114/74 A, 220/9 LG v B63b 25/16 114/74 A, 74R, 74 T;

space between the primary tank and the spray shield for enabling the passage of seepage from upper portions of the primary tank through the space and into the drip pan.

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sum 3 0r 3 1 4 ATTO'RNEY INVENTOR M475)? 6. 60 453 CONTAINER FOR LIQUEFlED GASES AT CRYOGENIC TEMPERATURES This invention relates to insulated containers and more particularly to an improved minimum cost, maximum safety, insulated container suitable for the storage of liquefied gases at atmospheric pressure and cryogenic temperatures in a tanker vessel.

It is desirable to transport many substances which normally exist in gaseous form as liquids. As in the case of methane, which liquefies at 259 F, these liquid materials must be transported at cryogenic temperatures. Storage and transport at these ultra-low, cryogenic temperatures, of course, present many materialhandling problems.

For example, ordinary carbon steel such as that normally used in ship construction is quite susceptible to embrittlement at low temperatures, and such embrittlement can lead to fracture of hull structures. It is therefore extremely important that cryogenic, liquefied gases be isolated from contact with the hulls of the vessels in which they are transported.

Prior art attempts to prevent these cryogenic liquids from coming into contact with ship s hulls have included construction of a fully redundant double-wall tank having an inner and an outer liquid-tight barrier, with each wall being of sufficient structural integrity to withstand the entire dynamic and static loads of the liquid contents of the tank. While this technique achieved a maximum degree of safety, this was accomplished only at high cost and the second or outside barrier was useful only in theevent of rupture of the inner or primary barrier.

Prior art tank designs that have incorporated drip pans to collect seepage have required the complete installation of the drip pan and the adjacent hull structure before the installation of the primary tank is begun. This construction sequence has been because the primary tank and the drip pan have often been of different materials and shapes, or because the drip pan has been attached to and/or supported by the inner hull of the ship. Use of these construction procedures may result in damage to the drip pan and theadjacent ship structure in the subsequent installation of the primary tank.

It is, therefore, an object of the present invention to provide an improved, low cost, insulated cargo container for storage of liquefied gases. at cryogenic temperatures. 1

Another object is to provide such a cargo container that is easy and inexpensive to install. 1

Additional objects and advantages of the invention will be setforth in part in the description which follows, and in part will be obvious from the description, or may belearned by practice of the invention. These objects and advantages are realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

I To achieve these objects the present invention provides a liquefied gas container that meets the highest safety standards while retaining the economical features of single-wall tank construction. The container includes a primary tank for containing the liquefied gas and a drip pan, formed below and as an integral part of the primary tank. The drip pan collects and retains liquefied gas that leaks through the primary tank, and provides support for the bottom of the primary tank.

Because the drip pan is constructed of the same material as the primary tank, the erection of the primary tank and construction of the adjacent ship structure can proceed simultaneously. It is. therefore not necessary, as with prior art arrangements, to complete construction of the adjacent ship structure and the drip pan before the erection of the primary tank is commenced. As a result, thedrip pan and adjacent ship structure are notsubject to damage during construction of the primary tank.

The primary tank and the drip pan are preferably cylindrical in shape, and'the primary tank is preferably defined by a substantially conical top. Such cylindrical construction uses material more efficiently for any given volume of storage capacity than other shapes, such as prismatic tanks,,for example. Further, cylindrical tanks are far easier and less expensive to construct than other previously used shapes. A cylindrical tank uses about 30 percent less material than a prismatic tank for any given volume of storage capacity, and less expensive material is required since material in plate form is less expensive than profile sections.

Cylindrical tanks are also easier to construct than sphericaltanks because no compound forming is required, fewer welded joints are needed, and structural fit-up, staging, and erection is easier.

The container device of this invention includes a secondary barrier structure which includes the drip'pan vided within the drip pan space to provide structural I reinforcement as well as to provide baffles to minimize motion of any liquefied gas that might have leaked from the primary tank and collected in the drip pan.

The entire spray shield and the insulation surrounding it are supported by theprimary tank. Thus, it is not necessaryito provide an inner hull in thevessel as is required with other systems where thesecondary barrier normally is supported on the inner face of the inner hull. As a result, it is possible to simplify the structure of the ship, reduce costs'and construction time and arrange ballast spaces in a manner thatprovid'es optimum stability characteristics. 1 i I; i i 1 r As embodied and broadly described, the present invention includesa primary tank of predetermined wall thickness for containingliquefied gas, a drip' pan coextensive with .the primary tank and formed as an integral part of and below the primary tank for collecting and retaining quantities of the liquefied gas that may leak through the primary tank and for supporting the primary tank; a spray shield larger than and substantially similar in shape to the primary tank surrounding the lateral wallsand top and spaced from the primary tank for deflecting seepage from upper portions of the primary tank, the spray shield extending down below the bottom of the primary tank in partial spaced relation relative to the lateral walls of the drip pan; thermally conductive structural means in fixed spaced relation around the primary tank for holding the spray shieldin position and for maintaining a low thermal gradient between the primary tank and the spray shield; and thermal insulation applied externally to the drip pan and to the spray shield.

Preferably, the walls of the drip pan are of a thickness substantially equal to the thickness of the walls of the primary tank and the drip pan extends only directly beneath the primary tank to act as an integral support.

In accordance with the invention, apertures are provided in the drip pan in fluid communication with the space between the primary tank and the spray shield for enabling the passage of seepage from upper portions of the primary tank through the space and into the drip pan. Keying means are also provided in operative relationship with the hull and the container for permitting relative movement between them, to avoid transmission of stresses from the hull to the container. Supports are also located between the drip pan and the hull for transmitting the static load of the container and liquefied gas cargo to the tankers hull.

Preferably, the supports include a stool piece secured to the hull of the tanker and a bearing member secured to the underside of the drip pan and resting on the stool piece in sliding surface-to-surface contact. This arrangement permits unrestrained movement of the primary tank as it undergoes dimensional changes resulting from cooling to thetemperatures of the liquefied gas or warming to ambient temperature.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate presently preferred embodiments of the invention, and together with the description, serve to explain the principles of the invention.

Of the drawings:

FIG. 1 is a top plan view of a tanker vessel incorporating the containers of this invention;

FIG. 2 is a cross-section taken substantially on the line 2-2 in FIG. 1;

FIG. .3 is across-section taken substantially on the line 3-3 of FIG. 1;

FIG. 4 is a fragmentary cross-section taken substantially on the line 44 in FIG. 1;

FIG. 5 is a fragmentary cross-section taken substantially on the line 55 in FIG. 4; Q

FIG. 6 is a fragmentary cross-section taken substantially on the line 66'of FIG. 4;

FIG. 7 is an expanded detailed view of the structural means separating the primary tank and the spray shield of the invention; T

FIG. 8 is partially a schematic and partially a fragmentary cross-section taken substantially on the line 8-8 in FIG. 1; I

FIG. 9 is a fragmentary cross-section taken substantially on the line 9-9 in FIG. 8;

FIG. 10 is a top plan view of an alternative embodiment of a container showing one keying arrangement;

FIG. 1 1 is a fragmentary cross-section taken substantially on the line l1ll in FIG. 10;

FIG. 12 is a fragmentary cross-section taken substantially on the line l2-12 in FIG. 11;

FIG. 13 is a cross-section taken substantially on the line 13--l3 in FIG. 3;

FIG. 14 shows an alternative embodiment of the arrangement shown in FIG. 13; and

FIG. 15 shows an alternative embodiment of the structure shown in FIGS. 13 and 14.

With reference now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIGS. 1 and 2 a tanker vessel 20 having an outer hull 22 and a plurality of containers 24 for storing liquefied gases at cryogenic temperatures in accordance with this invention. The tanker is of conventional form and material and may be of a complete double skin type or may be of single skin construction with a double bottom and upper ballast tanks (not shown) as necessary to provide proper operating draft and stability characteristics in the ballast condition. Containers 24 are preferably cylindrical in configuration and are vertically oriented with the vertical central axis of the containers located on the longitudinal center line of the tanker.

In accordance with the invention, a primary tank of predetermined wall thickness is provided for containing liquefied gas. As here embodied, primary tank 26 (FIG. 3) is preferably constructed with a substantially conical top 28 and with a dome 30 protruding through the upper deck 32 of the tanker. Tank 26 may be constructed of aluminum alloy, 9 percent nickel-steel, or other material having suitable physical properties for containment of the liquefied gas cargo at cryogenic temperatures. The tank wall is preferably designed as a membrane structure and is essentially unstiffened, except as necessary to limit stresses due to local bending, or the effects of dynamic loads.

In accordance with the invention, a drip pan is formed as an integral part of and below the primary tank for collecting and retaining quantities of the liquefied gas that may leak through the primary tank and for supporting the primary tank. As here embodied, drip pan 34 is made of the same material as primary tank 26. Preferably, the drip pan extends only directly beneath the primary tank and the walls of the drip pan are of a thickness substantially equal to the predetermined wall thickness of primary tank 26. The drip pan is also cylindrical in shape so as to extend only directly beneath the primary tank and to have a minimum surface area. As

a result of theintegral structure of the primary tank and the drip pan and because they are made of the same material, the erection of the primary tank and drip pan can proceed simultaneously with the construction of I the adjacent ship structure. It is not necessary to first complete the drip pan and the adjacent ship structure, and the drip pan and the adjacent shipstructure are not subject to damage by later erection of the primary tank.

A spray shield is provided partially surrounding and spaced from the primary tank for deflecting seepage from upper portions of the primary tank into the drip pan. The spray shield is larger than and substantially similar in shape to the primary tank. As here embodied, the spray shield is a thin sheet or sheets 36 (FIGS. 3 and 4) and is constructed of the same material as the primary tank.

Thermally conductive structural means are provided in fixed spaced relation around the primary tank for holding the spray shield in position and for maintaining a low thermal gradient between the primary tank and the spray shield. As here embodied, the thermally conductive structural means are furring or spacing members 38 (FIGS. 6 and 7) that are secured to primary tank 26 by threaded studs 40. Members 38 can, of course, also be secured to tank 26 by welding or any other conventional securing arrangement. The spacing members are made of thermally conductive metal or other suitable material so that primary tank 26 and spray shield 36 operate at substantially the same temperature, with no substantial thermal gradient between them. The requirements for elaborate differential expansion compensation means between the primary tank and the spray shield, that would have to be provided if the primary tank and spray shield were thermally insulated from each other, are thereby eliminated.

Thermal insulation 42 (FIGS. 4-7) of polyurethane foam, P.V.C. foam, fiberglass, or similar materials, is secured to the outer surface of spray shield 36 and drip pan 34 to avoid overcooling and embrittlement of the ships hull. Sheathing 44 is applied to the outside surface of insulation 42 to protect it from physical damage or water in the event a leak develops in an adjacent ballast tank (not shown) or the ships hull. This sheathing may be of aluminum, plywood, or similar material.

Spray shield 36 is preferably constructed of the same material as the primary tank and may be welded, bolted, riveted or otherwise secured to the spacing members 38. Insulation 42 may be applied by spraying or, in the alternative, fixed to the spray shield and drip pan in a series of panels.

' Drip pan 34 is made of sufficient depth to permit easy access to it for construction and inspection. The drip pan includes a cylindrical side surface 50 (FIG. 4) that is co-planar with the sides of primary container 26. A plurality of apertures 52 are provided in side wall 50, and in fluid communication with the space 54 between primary tank 26 and spray shield 36 for enabling the passage of seepage from upper portions of the primary tank through space 54 and into drip pan 34. I

The drip pan space56 includes a plurality of girders 58 (FIGS. 4, 5, 13, 14, and that extend between drippan 34 and the bottom .60 of primary tank 26. These girders act to strengthen the container as well as to minimize motion of any liquified gas that has seeped into the drippan from the primary tank and include spaced apertures 61 (FIGS. 4 and 5 adjacent the lower surfaceof the drip pan. Of course, the minimization of motion of the liquefied gas in the drip pan contributes to stability of the ship.

Alternativeembodiments of girders 58 may be utilized, as illustrated in FIGS. 13-15. FIG. 13 illustrates a configurationin which girders 58 are spaced in para]- l el relationship to one another. FIG. 14 shows an alternative embodiment wherein the girders are arranged in a radial configuration emanating from the center of the primary tank, and FIG. 15 illustrates still another embodiment wherein the girders are in spaced annular configuration.

gas. Several alternative configurations of suitable keying means are shown in the drawings. Preferably, one set of keys 74 (FIG. 13) are provided between the bottom of drip pan 34 and the inner bottom 76 (FIG. 3) ofthe ship, and another set 78 (FIGS. 8 and 9) is located between the sides of dome 30 and the adjacent structure of the ships deck 32.

The bottom set of keys comprises one key/keyway arrangement 74-75 at the longitudinal centerline of the ship to restrain athwartship motion of the primary tank. Another key/keyway arrangement is located at the transversecenterline of the primary tank to secure the tank against longitudinal motion. Similarly, tank dome 30 is secured against relative motion by means of keys 78 located in keyways 80. The keys need not necessarily be oriented in line with the principal axes of the ship, nor need they be limited to the two sets at the top and bottom described. Additional sets may be provided either at the top or bottom of primary tank 26, if desired, to reduce unit bearing loads, or the orientation may be varied for optimum efficiency or to achieve a desirable relationship with adjacent ship structure.

An alternative key-keyway arrangement is shown in FIGS. 10-12, and includes a plurality of keyways 84 integral with/or structurally connected to the conical top surface 28 of'primary tank 26. Keys 82 are provided in integral relationship with/or structurally coupled to the ship structure.

Supports are provided between the drip pan and the hull of the tanker for transmitting the static load of the container and liquefied gas cargo to the tankers hull.

. As here embodied, the supports include a stool piece from cooling (to the temperatures of the liquefied gas) Keying means are also provided in operative relationor warming (to ambient temperature). Either the stool piece or the bearing member, or both, may befaced witha material especially suited as a bearing/sliding surface to permit unrestrained movement of primary tank 26.

Alternative arrangements of the supports may be provided as illustrated in FIGS. 14 and 15. In FIG. 14

the supports are provided beneath and in line with radially extending girders 58, and in FIG. 15 the supports are provided'beneath and in line with the spaced annular configuration of girders 58.

Still another strengthened embodiment (not shown) combines the radially extending girders (FIG. 14) with the annular configuration of girders (FIG. 15), and supports are provided beneath and in line with each of these girders.

An important feature of the container of this invention is thatboth the supports and the keying means are located externally to the spray shield or secondary barrier in the preferred embodiments, and therefore, do not compromise the integrity of the spray shields containment of seeping liquefied gas.

Another feature strengthens the overall structure and particularly the bottom keys 74 by locating reinforcing girders (not shown) within keys 74 and directly below and in line with the annularly positioned girders 58 of FIG. 15.

It is desirable to maintain a nitrogen atmosphere in the space 100 (FIG. 8) surrounding the container, in the space 54 between primary tank 26 and spray shield 36, and within the drip pan. Such a nitrogen atmosphere may be provided by nitrogen source 102 connected to pump 104 which feeds nitrogen under pressure through conduit 106 into the spaces 100 and 54.

Thus, the present invention provides for a unique container for liquefied gases at cryogenic temperatures for use in a tanker. The invention in its broader aspects is not limited to the Specific details shown and described and departures may be made from such details without departing fromthe principles of the invention and without sacrificing its chief advantages.

I claim:

1. A device for containing liquefied gases at cryogenic temperatures in a tanker, comprising:

a primary tank for containing the liquefied gas;

a drip pan formed as an integral part of and below said primary tank for collecting and retaining liquefied gas that leaks from said primary tank and for supporting said primary tank, said drip pan extending only directly beneath said primary tank and having apertured side walls coextensive with the side walls of said primary tank;

a spray shield which is structurally separate from, larger than and substantially similar in shape to said primary tank, said shield surrounding and spaced from said primary tank for deflecting seepage from upper portions of said primary tank into said drip pan through its apertured side walls which are in fluid communication with the space between said primary tank and said spray shield;

thermally conductive structural means in fixed spaced relation around said primary tank for holding said spray shield in position and for maintaining a low thermal gradient between said primary tank and said spray shield; and

thermal insulation secured externally to said drip pan and to said spray shield.

2. A device as in claim 1 wherein said primary tank and said drip pan are each substantially cylindrical.

3. A device as in claim 1 further including:

keying means in operative relationship with the tankers hull and said container device for permitting relative movement between said hull and the container device.

4. A device as in claim 3 further including:

supports located between said drip pan and the hull of said tanker for transmitting the load of said container device and liquefied gas cargo to the tankers hull.

5. A device as in claim 1 including a plurality of girders extending between the lower surfaces of said primary tank and said drip pan and wherein said girders include spaced apertures therein whereby said girders strengthen said container device and act as baffles to minimize motion of said liquefied gas within the drip pan.

6. A device as in claim 5 wherein said girders are in spaced parallel relationship with one another.

7. A device as in claim 5 wherein said girders are in spaced annular configuration.

8. A device as in claim 5 wherein said girders are in a radial configuration emanating from the center of said primary tank.

9. A device as in claim 5 wherein said drip pan comprises substantially thesame material as said primary tank.

10. A device as in claim 1 wherein the side walls of said drip pan are substantially the same thickness as the side walls of said primary tank.

11. A device as in claim 1, wherein said drip pan is of sufficient depth to permit access thereto. 

1. A device for containing liquefied gases at cryogenic temperatures in a tanker, comprising: a primary tank for containing the liquefied gas; a drip pan formed as an integral part of and below said primary tank for collecting and retaining liquefied gas that leaks from said primary tank and for supporting said primary tank, said drip pan extending only directly beneath said primary tank and having apertured side walls coextensive with the side walls of said primary tank; a spray shield which is structurally separate from, larger than and substantially similar in shape to said primary tank, said shield surrounding and spaced from said primary tank for deflecting seepage from upper portions of said primary tank into said drip pan through its apertured side walls which are in fluid communication with the space between said primary tank and said spray shield; thermally conductive structural means in fixed spaced relation around said primary tank for holding said spray shield in position and for maintaining a low thermal gradient between said primary tank and said spray shield; and thermal insulation secured externally to said drip pan and to said spray shield.
 2. A device as in claim 1 wherein said primary tank and said drip pan are each substantially cylindrical.
 3. A device as in claim 1 further including: keying means in operative relationship with the tanker''s hull and said container device for permitting relative movement between said hull and the container device.
 4. A device as in claim 3 further including: supports located between said drip pan and the hull of said tanker for transmitting the load of said container device and liquefied gas cargo to the tanker''s hull.
 5. A device as in claim 1 including a plurality of girders extending between the lower surfaces of said primary tank and said drip pan and wherein said girders include spaced apertures therein whereby said girders strengthen said container device and act as baffles to minimize motion of said liquefied gas within the drip pan.
 6. A device as in claim 5 wherein said girders are in spaced parallel relationship with one another.
 7. A device as in claim 5 wherein said girders are in spaced annular configuration.
 8. A device as in claim 5 wherein said girders are in a radial configuration emanating from the center of said primary tank.
 9. A device as in claim 5 wherein said drip pan comprises substantially the same material as said primary tank.
 10. A device as in claim 1 wherein the side walls of said drip pan are substantially the same thickness as the side walls of said primary tank.
 11. A device as in claim 1, wherein said drip pan is of sufficient depth to permit access thereto. 